Process for the production of hydroxylammonium salts

ABSTRACT

Process for the production of hydroxylammonium salts by reduction of nitric oxide with hydrogen in dilute mineral acid solution in the presence of noble-metal catalysts and modifiers such as formic acid, water-soluble formates, oxalic acid, chloral hydrate or carbon monoxide.

O United States Patent [151 3,649,170

Heine et al. 1 Mar. 14, 1972 [54] PROCESS FOR THE PRODUCTION OF [58]Field of Search ..23/50, 87, 102, 105, 117, 190, HYDROXYLAMMONIUM SALTS23/190 A [72] Inventors: Heinz Heine; Rudolf Gerken, both of Far- [56]References Cited benfabriken Bayer AG, Krefled-Uerdingen, Germany UNITEDSTATES PATENTS [22] Filed: Jan. 21, 1970 2,628,889 2/1953 Benson..23/190 A [21] AppL No 4,448 2,719,778 10/1955 Jockers ..23/190 ARelated s Application Data Primary Examiner-Earl C. ThomasAttorney-Connol1y and Hutz [63] Continuation of Ser. No. 607,882, Jan.9, 1967, abandoned- 57 ABSTRACT 30 Foreign Application priority DataProcess for the production of hydroxylammonium salts by reduction ofnitric oxide with hydrogen in dilute mineral acid Jan. 21, 1966 Germany..F 48222 Solution in the presence f noblemeta] catalysts and difi rsuch as formic acid, water-soluble formates, oxalic acid, [52] U.S. Cl..23/50, 23/87, 23/102, chloral hydrate or carbon monoxide 23/105,23/117, 23/190 A [51] Int. Cl. ..C01b 21/14 4 Claims, No DrawingsPROCESS FOR THE PRODUCTION OF HYDROXYLAMMONIUM SALTS This application isa continuation of application, Ser. No. 607,882 filed Jan. 9, 1967 andnow abandoned.

FIELD OF THE INVENTION This invention relates to a process for theproduction of hydroxylammonium salts.

DESCRIPTION OF THE PRIOR ART It is known that hydrogen and nitric oxidecan be reacted in an acid medium on noble-metal catalysts tohydroxylammonium salts (German Pat. No. 968,363 and GermanAuslegeschrift No. 1,177,118). It is also known that with decreasingsulfuric acid concentration (or with increasing hydroxylammonium saltconcentration) the extent of side reactions, especially the formation ofammonium salts increase. Various processes have been proposed to improvethe selectivity of the reaction. Other suggestions relate to improvedcatalysts, especially with additives introduced either during orfollowing the preparation of the catalyst. One proposed improvement inthe reaction velocity and hence in the yield per unit of volume and timeis described, for example, in German Pat. specification No. 885,396,according to which the catalytic reaction is carried out in the presenceof organic compounds containing polar groups and an average number offrom four to carbon atoms per molecule.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a process for the production of hydroxylammonium salts with highyields. It is another object of the present invention to provide aprocess for the production of hydroxylammonium salts, wherein thecatalysts are maintained at high selectivity and activity. Other objectswill be described in the following description.

A process for the preparation of hydroxylammonium salts from nitricoxide and hydrogen has now been found in which formic acid, watersolubleformates, oxalic acid, chloral hydrate or carbon monoxide is used asmodifier. In this process, the average selectivity and activity of thecommonly used catalysts is surprisingly higher, particularly when formicacid is added, while on the other hand the selectivity remains almostconstant and at a high level throughout the reaction, i.e., despite anincrease in the hydroxylammonium sulphate concentration. Particularemphasis is placed on this.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The quantities of theaforementioned modifiers may vary within relatively wide limits,although they are preferably added to the reaction solution inquantities of from 0.1 mMols to 4 Mols per liter.

The production of the hydroxylamine salts is carried out as known per seby introducing nitrogen oxide and hydrogen in an aqueous mineral acidsolution containing the suspended catalyst therein. In the discontinuousprocess, the synthesis gas is fed into the acid catalyst mixture untilthe acid is nearly consumed, whereby preferably a pH OF 2.5 is notexceeded, to avoid the formation of substantial amounts of ammonium orammonium salts. The hydroxyl-ammonium salts so obtained are, afterremoving the catalyst, either precipitated by cooling the reactionsolution or the reaction solution with the hydroxylamine salt containedtherein is directly used for synthesis, e.g., the production of lactams.The salts can also be used as reducing agents, as photographicdevelopers, as stabilizers, etc.

In the continuous process for the manufacture of hydroxylamine, into thereaction vessel fresh acid is conducted periodically or continuouslywhereby part of the reaction solution is removed together with thehydroxylamine salt formed. The process also can be carried out stepwise,whereby the reaction mixture is led from step to step, each step beingmaintained at a constant pH range. The first step starts with the freshacid, whereby from the last step the substantially neutralized reactionsolution together with the hydroxylamine salt is removed.

The reaction temperature is between 0 and C., preferably the reaction iscarried out at a temperature of between 40 and 60C. The concentration offree acid should amount to between 0.01 and 5.0 N; the molar ratio ofNOrH, is normally to be maintained at a range of between 1:15 and 1:3.0,preferably of between 1:16 and 112.0. For reason of economics, thereaction is performed at normal pressure, however, it is possible toapply superpressure also. As acids, the strong mineral acids such assulfuric acid, hydrochloric acid, phosphoric acid, nitric acid or thelike are used.

The metals of the platinum series and advantageously platinum itself maybe used as noble metal catalysts. Activated carbon or graphite can beemployed as an acid resistant support material for the noble metals.

The terms activity and selectivity used in this specification aredefined as follows: activity is the percentage of NO contained in thehydroxylammonium salt and the ammonium salt formed, based on the totalquantity of NO introduced, while selectivity is defined as 100 times theratio: mols of hydroxylammonium salt formed/total number of mols ofhydroxylammonium salt and ammonium salt formed.

The invention is illustrated by the following examples:

EXAMPLE I 250 mg. of Pt, in the form of a 1% Pt-Catalyst, based ongraphite, are introduced into 1 liter of 20% sulfuric acid. A mixture of12.5 1. of NO and 25 l. of hydrogen per hour is then introduced withstirring in a constant stream at a temperature of from 40 to 45C. Every2 hours, the solution is analyzed for hydroxylammonium sulfate andammonium sulfate, the results being given as activity and selectivityvalues for the corresponding time interval. Total duration of test 8hours. Activity pattern at 2-hour intervals: 85, 85, 47, 40; average 64.Selectivity pattern at 2-hour intervals: 58,57,17,0; average 33.

During the final two hours, almost 20% of the hydroxylammonium sulphatepreviously formed was degraded again.

EXAMPLE 2:

The procedure is as in Example 1, except that 25 mM. of formic acid wereadded before the beginning of synthesis. Total duration of test 8 hours.

Activity pattern at 2-hour intervals: 84, 79, 79, 80; average 8 lSelectivity pattern at 2-hour intervals: 96, 96, 96, 99; average 98.

EXAMPLE 3;

The sulphuric acid catalyst suspension prepared in accordance withExample 1 is heated for 3 hours to 95C. following the addition of 3 g.of oxalic acid. It is then cooled to 40C., after which the procedure isas described in Example 1. Total duration of test 8 hours.

Activity pattern at two-hour intervals: 88, 80, 77, 72; average 79.

Selectivity pattern at two-hour intervals: 69, 73, 72, 57; average 68.

EXAMPLE 4:

The procedure is as described in Example 1, except that, before thebeginning of synthesis, carbon monoxide is bubbled through the catalystsuspension at a rate of 20 l./hr. for 15 minutes, and thereafter for aperiod of 1 minute every 2 hours. Total duration of test 8 hours.

Activity pattern at 2-hour intervals: 75, 56, 65, 44; average 60.

Selectivity pattern at 2-hour intervals: 68, 46, 81, average 68.

ous mineral acid solution of formic acid, oxalic acid or carbonmonoxide.

2. The process according to claim 1 wherein the reaction is conducted inthe presence of carbon monoxide.

3. The process according to claim 1 wherein the reaction is conducted inthe presence of formic acid.

4. The process according to claim I wherein the reaction is conducted inthe presence of oxalic acid.

2. The process according to claim 1 wherein the reaction is conducted inthe presence of carbon monoxide.
 3. The process according to claim 1wherein the reaction is conducted in the presence of formic acid.
 4. Theprocess according to claim 1 wherein the reaction is conducted in thepresence of oxalic acid.